The incident occurred early Saturday morning when a fishing boat from China’s Guangdong Province was detected fewer than 25 nautical miles from Taiwan’s Penghu island chain. The Chinese vessel refused to stop for inspection, Taiwan’s Coast Guard Administration reported, despite several radio warnings.

When crew members tried to prevent Taiwan’s officers from boarding their boat, the coast guard fired on the craft with rubber bullets, injuring two crew members, Focus Taiwan reports. The injured were taken to hospital for treatment and are in stable condition. The coast guard took control of the vessel and Taiwanese authorities detained the five other crewmembers onboard.

“This shooting incident… is outrageous,” spokesman An Fengshan of China’s Taiwan Affairs Office said in a statement. “We asked Taiwan to immediately investigate and solve the problem, as well as release the [mainland] ship as soon as possible,” it continued.

An said Taiwan had disrespected the crew’s rights to traditional fishing grounds and called for their quick release, the South China Morning Post reports.

The Penghu archipelago lies about 50 kilometers from Taiwan’s main island, and about 140 kilometers from China’s coast.

Taiwan’s Mainland Affairs Council noted that despite China’s moratorium on fishing boats, the powerhouse doesn’t seem to be stopping its boats from breaking its own rules.

“Mainland fishing boats have violated Taiwan’s law and repeatedly engaged in illegal fishing, seriously affecting Taiwanese fishermen’s rights and interests,” MAC said, according to Focus Taiwan. It suggested Beijing “educate” its fishermen to prevent further incidents.

Taiwan’s Coast Guard Administration says the island state chased more than 100 Chinese fishing vessels out of its waters last year, and it has raised fines for such trespassing to more than $331,000. Patrols have been stepped up under President Tsai Ing-wen, who is seen as pro-Taiwanese independence.

Taiwan stopped, detained and fined crews from at least two fishing boats from Hong Kong and the mainland in March.